Using panel village census data from Senegal, we assess the impact of a decentralized agricultural development program—the Programme de Services Agricoles et Organisations de Producteurs (PSAOP)—on membership and assortative matching in community-based organizations (CBOs). We find that channeling agricultural assistance through CBOs makes these organizations more inclusive in the sense that several tradition-bound assortative matching patterns are broken: homophily in ethnicity and wealth are reduced. Traditionally marginalized groups such as men of nomadic background, women with small landholdings and little education and those residing in female-headed households become CBO members whereas the position of previous CBO leaders is not reinforced. Similarly, those households that received services from a CBO before the PSAOP was in place are less likely to stay. This leads to more heterogeneous CBOs and is in line with the terms and conditions of the program. On the other hand, the likelihood of CBO membership is reduced in project villages, with significant differences between men and women. Women disproportionately drop out of CBOs which receive PSAOP benefits. We conclude that for grassroots-level development projects to be successful, contextual factors need to be integrated into program design and implementation, since they shape local participation. Understanding local power relations and the potential for changing preferences due to external support are key to inclusive participation and development at the local.